The page the user is sent to, "index1," has no extension. This causes it to be served up without a MIME type. Internet Explorer assumes that files without MIME types are text/html; Firefox assumes text/plain. To fix the problem, just rename index1 to index1.htm.
/EDIT: Actually, the server is serving it up explicitly as text/plain. IE shouldn't see this properly. Anyway, renaming it will still work.